1. Field of the Invention
This invention relates to a structure of treating the terminal (end) of a shield wire (hereinafter referred to as "a shield wire's terminal treatment structure, or terminal treatment structure", when applicable) which may be connected to a variety of electrical devices such as an electric motor in an electric car for instance.
2. Description of the Related Art
In general, in the case where a current supplying wire or control signal wire is connected to an electric device mounted on a vehicle such as an electric car, it is often required to subject the wire to electro-magnetic shield treatment or water-proof treatment. The electro-magnetic shield treatment is performed to prevent the electric device from being made unstable in operation by a variety of noises. The water-proof treatment is performed to prevent the electrical contact portion or the like from being damaged by water drops or the like which may enter the electric device along the electric wire.
An example of the above-described conventional electro-magnetic shield treatment or water-proof treatment is a terminal treatment structure 100 as shown in FIG. 8.
The terminal treatment structure 100 is designed as follows: A shield electric wire 101 with a braid 104 exposed, is inserted into a water-proof grommet 115 under pressure, and then inserted in a metal casing 111 of an electrical device or the like. Inside the metal casing, a conductor 102 covered with an insulating cover 103 is extended as long as required for wiring from the end portion of the braid 104. A connecting terminal 110 such as a crimping terminal, which is to be connected to a terminal (not shown) of the electrical device, is secured to the conductor 102.
In the terminal treatment structure 100, the water-proof treatment is as follows: The water-proof grommet 115, which is made of insulating material such as synthetic rubber, is put on the shield wire 101, and the grommet 115 is press-fitted in the metal casing 111 to keep an outer cover 105 water-tight in the metal casing 111.
The electro-magnetic shield treatment is as follows: A metal shield connection ring 118, which is connected to the braid 104, is mounted on the end of the water-proof grommet 115, so that the braid 104 is electrically connected to the metal casing 111.
The shield connection ring 118 comprises: an inner cylindrical portion 119A which is inserted between the braid 104 and the insulating cover 103 covering the conductor 102 so that it is electrically connected to the braid 104; and an outer cylindrical portion 119B which covers the outer peripheral portion of the water-proof grommet 115 so that it is electrically connected to the metal casing 111. That is, the ring 118 is of a double-crown structure. Hence, the electro-magnetic shielding is achieved when the braid 104 of the shield wire 101 is electrically connected through the shield connection ring 118 to the metal casing 111.
In the above-described terminal treatment structure 100, as was described above the inner cylindrical portion 119A of the shield connection ring 118 is inserted between the insulating cover 103 and the braid 104, and the outer cylindrical portion 119B is arranged between the grommet 115 and the metal casing 111. Hence, the shield connection ring 118 acts to fix the whole terminal (end) of the shield wire 100, thus preventing the axial movement of the shield wire 100.
Hence, in the case where, in connecting the connecting terminal 110 to the connecting terminal of the electrical device, the conductor 102 covered with the insulating cover 103 is not long enough, so that it is impossible to adjust the length of the conductor 102.
Furthermore, it is impossible to provide simple locking means between the shield connection ring 118 and the water-proof grommet 115. Therefore, the shield connection ring 118 may be disengaged from the water-proof grommet 115. In this case, the electrical connection between the braid and the metal casing 111 is diminished. In order to eliminate this difficulty, in the conventional terminal treatment structure, as shown in FIG. 9, the metal casing 111 has a stepped wire inserting inlet 112. The shield connection ring 118 is abutted against the wire inserting inlet 112 so that the shield connection ring 118 may not come off the water-proof grommet 115. However, the above-described conventional structure is disadvantageous in that the metal casing 111 must be machined, and accordingly the structure is high in manufacturing cost.